There are many medical treatments that involve instances of cutting, ablating, coagulating, destroying, or otherwise changing the physiological properties of tissue. These techniques can be used beneficially to change the electrophysiological properties of tissue, such as those associated with cardiac arrhythmias or other electrophysiological abnormalities. In particular, normal sinus rhythm of the heart begins with the sinoatrial node (“SA node”) generating a depolarization wave front. The impulse causes adjacent myocardial tissue cells in the atria to depolarize, which in turn causes adjacent myocardial tissue cells to depolarize. The depolarization propagates across the atria, causing the atria to contract and empty blood from the atria into the ventricles. The impulse is next delivered via the atrioventricular node (“AV node”) and the bundle of HIS to myocardial tissue cells of the ventricles. The depolarization of cells propagates across the ventricles, causing the ventricles to contract. This conduction system results in the described, organized sequence of myocardial contraction leading to a normal heartbeat.
Sometimes, anatomical obstacles such as fibrosis, fibrotic scar, or uneven distribution of refractoriness of cardiac myocytes in certain parts of the heart in the atria or ventricles can lead to aberrant conductive pathways in heart tissue that disrupt the normal path of depolarization events. These anatomical obstacles or “conduction blocks” can cause the electrical impulse to degenerate into several circulating wavelets that circulate about the obstacles. The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms called arrhythmias. An arrhythmia can take place in the atria, for example, as in atrial tachycardia, atrial fibrillation (“AF”), or atrial flutter. The arrhythmia can also take place in the ventricle, for example, as in ventricular tachycardia. Additionally, there may be ectopic sites within the heart that produce premature activations from such tissue sites, producing arrhythmogenic conduction patterns.
One approach to treating an arrhythmia includes creating one or more lesions that compartmentalize the aberrant pathway and direct electrical conduction along selected pathways to promote organized signal conduction, while also isolating AF triggers from connecting with the atria. Often, the application of energy is used to destroy cells at the ablation site while leaving the surrounding structures of the organ largely intact. Radiofrequency (“RF”) energy and cryogenic cooling have been found to be highly viable in this regard, and are commonly employed. Other ablative techniques include the application of ultrasound, microwave, laser, cytotoxic agents, etc.
However, there may be potential drawbacks associated with the application of RF energy. One such potential drawback is that the application of RF energy to a target tissue site may have effects on non-target tissue. For example, the application of RF energy to atrial wall tissue may cause collateral damage in the esophagus or phrenic nerve, which are typically located proximate the heart. Further, RF ablation procedures may require an extended period of treatment time before the arrhythmia is corrected, which can increase the likelihood of collateral damage to non-target tissue or the occurrence of tissue charring, which could result in an embolic event.